A friend of mine brought over his ADT pushbutton panel the other day, reporting it "not working". It is fed from the back either by a 4.5V power-supply (wall-wart) or 3 x AA batteries in a pocket between the body and the wall-mount. Two things had happened:
a) The little SMT power-jack had pulled away on two of the four tabs. That was a quick fix.
b) In some previous time, one of the batteries had leaked and there was a large build-up of green salts concealed under the batteries.

He had installed new batteries, but the salts had bridged connections, causing them to short. I used an electric drafting eraser and dental picks to get all the corrosion out and soldered over the traces. It works.
NOTE: Those salts are deliquescent - meaning that they attract water out of the air - so no surprise on the migration.

Peter Wieck
Melrose Park, PA